The present invention relates to telecommunication technology, and more particularly, to a method and apparatus for pulse communication.
It is well known that telecommunication technology is a technology concerning the producing, processing, exchanging, recording, dubbing, transmitting, transferring, and receiving of electrical signals. Since the electrical signals are information carriers, telecommunication technology is also called "electrical signal transmission technology". Information such as character, data, voice, image, sensor signal, etc is included in all the source signals to be transmitted. Different communication systems such as telegraphs, telephones, broadcasts, faxes, televisions, radars, remote controls, romote sensing, artificial intelligence have different source signal. A communication system usually comprises an information source, a converter, a channel, a reverse convertor, and an information destination, etc., and normally can be generlized into three parts: information transmitter, information receiver and channel. Up to now, the rectangular pulse communication method has been used in pulse communication systems.
Conventional systems using rectangular pulse communication methods have the disadvantage of occupying a very wide bandwidth. Even the square pulse, which has the best spectrum characteristics of all the rectangular pulses, a bandwidth of 9 times the fundamental--frequency bandwidth is required in order to assure good communication quality. This requirement can hardly be met in actual communication system. In order to carry out communication, the basic shape of all kinds of pulse must be maintained. Therefore, they should at least consist of a fundamental frequency and its lowest harmonic (in order to facilitate description, this kind of combined wave is refered to below as fundamental low wave). From the spectrum expression of a square pulse, EQU I(t)=1/2+2/.pi.[cos .omega.t-1/3 cos 3.omega.t+1/5 cos 5.omega.t-1/7 cos 7.omega.t+ . . . +(-1).sup.n /2n+1 cos (2n+1).omega.t+ . . .]
it can be inferred that the bandwidth of its fundamental low wave is three times that of its fundamental frequency.
Since rectangular pulse occupy very wide bandwidth, communication system using these type of pulses also have the following disadvantages:
1. In the course of transmission, power loss is heavy, pulse deformation is severe, and the ratio of signal to noise is low. In addition, intersymbol interference is heavy, and transmission distance is short, too. The longest transmission distance (to a singal station) is only 1.7 kilometers, and the number of possible relay stations allowed is also less than 10.
2. When using a rectangular pulse, the gain of the electrical device is small, and the transmitted power is low.